﻿using System;
using System.Collections.Generic;
using System.Web;

/// <summary>
///whoBase64 的摘要说明
/// </summary>
public class whoBase64
{
    byte[] source;
    int length,length2;
    int blockCount;
    int paddingCount;
    public whoBase64()
    {
        lookupTable = new char[64]
          {  'A','B','C','D','E','F','G','H','I','J','K','L','M',
            'N','O','P','Q','R','S','T','U','V','W','X','Y','Z',
            'a','b','c','d','e','f','g','h','i','j','k','l','m',
            'n','o','p','q','r','s','t','u','v','w','x','y','z',
            '0','1','2','3','4','5','6','7','8','9','+','/'};
    }
    public void Base64Encoder(byte[] input)
    {
      source=input;
      length=input.Length;
      if((length % 3)==0)
      {
        paddingCount=0;
        blockCount=length/3;
      }
      else
      {
        paddingCount=3-(length % 3);//need to add padding
        blockCount=(length+paddingCount) / 3;
      }
      length2=length+paddingCount;//or blockCount *3
    }

    public char[] GetEncoded()
    {
      byte[] source2;
      source2=new byte[length2];
      //copy data over insert padding
      for (int x=0; x<length2;x++)
      {
        if (x<length)
        {
          source2[x]=source[x];
        }
        else
        {
          source2[x]=0;
        }
      }
      
      byte b1, b2, b3;
      byte temp, temp1, temp2, temp3, temp4;
      byte[] buffer=new byte[blockCount*4];
      char[] result=new char[blockCount*4];
      for (int x=0;x<blockCount;x++)
      {
        b1=source2[x*3];
        b2=source2[x*3+1];
        b3=source2[x*3+2];

        temp1=(byte)((b1 & 252)>>2);//first

        temp=(byte)((b1 & 3)<<4);
        temp2=(byte)((b2 & 240)>>4);
        temp2+=temp; //second

        temp=(byte)((b2 & 15)<<2);
        temp3=(byte)((b3 & 192)>>6);
        temp3+=temp; //third

        temp4=(byte)(b3 & 63); //fourth

        buffer[x*4]=temp1;
        buffer[x*4+1]=temp2;
        buffer[x*4+2]=temp3;
        buffer[x*4+3]=temp4;

      }

      for (int x=0; x<blockCount*4;x++)
      {
        result[x]=sixbit2char(buffer[x]);
      }

      //covert last "A"s to "=", based on paddingCount
      switch (paddingCount)
      {
        case 0:break;
        case 1:result[blockCount*4-1]='=';break;
        case 2:result[blockCount*4-1]='=';
          result[blockCount*4-2]='=';
          break;
        default:break;
      }
      return result;
    }
    private char[] lookupTable;

    int GetKey(ref int i, ref int index)
    {
        int nKey = lookupTable[i] >> (8 - index);
        nKey = nKey << (6 - index);
        if (index>=2)
        {
            index = (index + 6) % 8;
            i++;
            nKey = nKey | (lookupTable[i] >> (8 - index));
            return nKey;
        }
        return 0;
    }
    public void SwapKey(byte[] s)
    {
        int nSelect = 6;
        for (int i = 0; i < s.Length;)
        {
            if (i+2>s.Length)
            {
                break;
            }
            else
            {
                int nFirestKey = GetKey(ref i, ref nSelect);
                int nSecondKey = GetKey(ref i, ref nSelect);
                char before = lookupTable[nFirestKey];
                lookupTable[nFirestKey] = lookupTable[nSecondKey];
                lookupTable[nSecondKey] = before;
            }
           
        }

    }

    private char sixbit2char(byte b)
    {


      if((b>=0) &&(b<=63))
      {
        return lookupTable[(int)b];
      }
      else
      {
        //should not happen;
        return ' ';
      }
    }
}
